1. Layer by layer solidification
Pure aluminum or eutectic aluminum alloys do not have a solidification zone where liquid and solid coexist during the solidification process, so the solid in the outer layer and the liquid in the inner layer are clearly separated by a boundary line (solidification front) on the cross-section. As the temperature decreases, the solid layer thickens and the liquid layer decreases, reaching directly to the center of the aluminum casting. This solidification method is layer by layer solidification.
2. Pasty solidification
If the crystallization temperature range of aluminum alloy is wide and the temperature distribution of aluminum castings is relatively flat, during a certain period of solidification, there is no solid layer on the surface of the casting, and the solidification zone where liquid and solid coexist runs through the entire section, similar to cement solidification, paste like solidification, and then solidification, which is called paste like solidification.
3. Intermediate solidification
Most solidification occurs between layer by layer and paste like solidification, known as intermediate solidification. Generally speaking, the quality of aluminum castings is closely related to their solidification method. Gold has strong filling ability, which is conducive to preventing shrinkage and porosity; Pasty solidification is the solidification method for obtaining compact aluminum castings.
In order to improve the quality of aluminum castings, increase labor productivity, and reduce costs, it is necessary to conduct a specific analysis of the aluminum castings and select a reasonable process plan when determining the casting process plan.